Ir camera and method for use with ir camera

Abstract

An infrared camera is arranged to compensate for temperature variations of the camera byRecording the output signal of each pixel of the detector during a shutter operation Using the recorded signal from each pixel to update a temperature offset map stored in the camera to ensure uniform signal levels at different camera temperatures, Said code means being arranged to perform the following steps during operation of the camera:save at least a first temperature offset map during a first shutter operation at a first temperature and a second temperature offset map during a second shutter operation at a second temperaturefit the data from the at least first and second offset maps to a curveusing the curve to compensate for variations in signal output caused by temperature variations.

Description

TECHNICAL FIELD [0001]The present invention relates to an IR camera and a method for use with an IR camera, to compensate for temperature changes of the camera during operation.BACKGROUND AND RELATED ART [0002]IR cameras are adapted to register incoming infrared radiation and present an image dependent on such radiation, typically displaying the temperature in various areas of the object. An IR camera typically comprises optics for focusing the radiation from an object onto a detector, such as a focal plane array. The focal plane array comprises a number of pixels, each pixel constituted, for example, by a microbolometer. The signal from a microbolometer type of focal plane array is related to the temperature of the microbolometer pixel structure. Each pixel is arranged to register incoming radiation in the infrared range, which causes an increase in temperature of the microbolometer. The temperature of the microbolometer is then converted into a signal output of the detector by mea...

AI Technical Summary

Benefits of technology

[0016]It is an object of the invention to provide a camera that will allow simpler manufacturing process.

[0029]Hence, the entire initial calibration of the camera can be performed at room temperature, simplifying the manufacturing process by avoiding the need to calibrate at different temperatures. Instead of attempting to make the focal plane array stable by calibration, the invention provides methods for compensating for the inherent instability of the focal plane array as the temperature varies during operation of the camera. The manufacturing environment can also be simplified, since the temperature does not have to be varied.

[0031]Using a default set of detector parameters will lead to differences in the pixel output depending on the ambient temperature, that is, the same pixel will produce different values for the same object temperature as the camera temperature changes. The change in signal output caused by ambient temperature changes may cause the output signal to saturate. The inventive solution is a way of avoiding saturation by comparing the signal level against an internal reference (shutter) and, if necessary, adjusting an internal detector parameter such as bias or offset in combination with a method to compensate temperature offset maps for the signal change caused by such changes in detector parameters.

[0035]According to an aspect of the invention a method is achieved for creating maps that can be used for compensation while the camera is operated, to avoid the need to create background temperature offset maps during calibration.

Problems solved by technology

Also, slight pixel-to-pixel differences in the microbolometer structure, which arise in the manufacturing of these devices, may cause different pixels to exhibit slightly different temperature dependent behaviour.

This will cause image quality degradation of the IR camera if not corrected for.

One drawback with such a solution is that it increases the power consumption and manufacturing cost of the focal plane array significantly.

This recording of temperature calibration data at different temperatures is a cumbersome and time-consuming part of the manufacturing process of an IR camera.

However, for focal plane arrays operating without a thermo electric cooler, the pixel-to-pixel signal output change, caused by heating of cooling of the focal plane array, may be so large that image quality is negatively impacted in a time frame which is shorter than the desired non-uniformity correction frequency.

Non-uniformity correction is typically still performed during operation of the infrared camera to compensate for pixel-to-pixel variations not fully corrected for by the data collected during calibration.

This procedure, referred to as temperature cycling, is cumbersome, and requires a complex calibration environment.

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